The manufacture of caustic soda (sodium hydroxide) by treatment of soda ash with lime is well known. This method of producing caustic soda generally is referred to in the art as the "causticization" process and involves reacting either soda ash with quick lime (calcium oxide) or soda ash with slaked lime (calcium hydroxide) to produce aqueous solutions containing 10 to 11 percent by weight of caustic soda. Illustrative of the use of the causticization process to produce caustic soda are the disclosures set forth in U.S. Pat. Nos. 2,979,380 and 4,451,443. For a disclosure of various plant operating designs based upon the use of the causticization process reference is made to Kirk-Othmer Encyclopedia of Technology, Vol. 1, ppgs. 740-748 (1964).
From a reading of the Kirk-Othmer reference cited above, it is clear that most caustic soda manufacturing operations, based upon the use of the causticization process, are associated with larger plant complexes for the manufacture of soda ash. One obvious reason for establishing caustic soda manufacturing operations in such close proximity to these larger plant complexes is the ready availability of the soda ash. Another is that the second reactant utilized in the causticization process; i.e., the lime, also is readily available from such soda ash manufacturing complexes as a co-product.
In contrast to the above, the present invention provides a process which can be operated, totally separated and apart from a soda ash manufacturing operation. More particularly, the present invention provides a process for the manufacture of caustic soda totally independent of a need for a separate source of both soda ash and lime.